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Re: (ITS#7974) LDBM's "laggard reader" flaw still present, in continue of ITS#7904
- To: openldap-its@OpenLDAP.org
- Subject: Re: (ITS#7974) LDBM's "laggard reader" flaw still present, in continue of ITS#7904
- From: firstname.lastname@example.org
- Date: Thu, 04 Dec 2014 10:31:14 +0000
- Auto-submitted: auto-generated (OpenLDAP-ITS)
Hallvard, thank for your comments.
2014-12-02 14:20 GMT+03:00 Hallvard Breien Furuseth <email@example.com>:
> On 10/23/2014 07:13 AM, firstname.lastname@example.org wrote:
>> Subject: [PATCH 1/2] lmdb: ITS#7974 oomkiller feature.
>> +typedef int (MDB_oomkiller_func)(MDB_env *env, int pid, void* thread_id,
>> size_t txn);
> Some thoughts about this:
> Instead of trusting the return value, it seems safer to re-check
> with mdb_reader_pid(). Like mdb_reader_check0() does. Maybe
> except on Windows, where file locks from dead processes may
> linger for a while until the OS reclaims them.
I agree that usign mdb_reader_pid() is a better way.
> Don't call it OOMkiller just because that's how you use it.
> Others might do something else, like sending a reader a signal
> which it interprets as "please wake up and finish your txn".
> Or it might decide this process is the one which should give up.
Could you suggest something other instead of "oomkiller"?
Be noted, the "dreamcatcher" feature has a critical bug, which I has
found and made fix while work on ITS#7968 & ITS#7987.
Currently we hard testing a new code.
So, in a week I plan to update both of the patches.
> This feature could make it interesting to let readers and writers
> tell each other things: Reserve some unused space in the reader
> table slots for stuff the reader's caller could put there, and
> some space for an impatient writer to leave a note. Could go
> in an independent commit if there is any demand for it though.
Communications between readers and writers may be interesting, but I
think it is over-engineering in the LMDB context.
IMHO the LMDB's code has a lot of technical debt, so it is more
usefull to re-implement all of from a scratch, under a rules of
May be I will do this, but on a basis and after a release of 1Hippeus
- it is a extreme performance engine for zero-copy mesaging in a
shared memory, partially like Intel DPDK.